ABSTRACT
The objective of this work is to develop a microwave assisted-ultraviolet (MW-UV) digestion in the presence of dilute HCl and H2O2 followed by ion chromatography (IC) measurements for the determination of total nitrogen in cereals. This approach (MW-UV-IC) requires lesser time and does not need environmentally hazardous materials as used in Kjeldhal method. Further, the developed method requires only microliter quantities of dilute HCl and few milliliters of H2O2 for the matrix digestion and simultaneous conversion of nitrogen to its ionic species for the subsequent analysis by IC. At the optimized acid concentrations (200 âµL of 0.1 âmol âL-1 HCl) and microwave power, the nitrogen in the cereals flours is converted to nitrate (NO3 -), nitrite (NO2 -) and ammonium (NH4 +) ions. The nitrogen species were separated using IonPac AS-20 and IonPac CS-17 columns and then quantified using suppressed conductivity detection. The method was applied to estimate the total nitrogen in flours of various cereals like; wheat (Triticum aestivum), rice (Oryza sativa), finger millet (Eleusine coracana), jowar (Sorghum) and pearl millet (Pennisetum glaucum). The results obtained using proposed method, were in good agreement with that of Kjeldhal method. Further, the precision of the values obtained by developed method was on par with the Kjeldhal method for all the tested flours as verified by F-test (n â= â5 and 95% confidence limit). Additionally, greenness assessment tools like analytical Eco-scale and green analytical procedure index (GAPI) suggested the proposed MW-UV-IC method, for the determination of total nitrogen in cereal flours, to be excellently green and safe.
ABSTRACT
Herein, we report a method for the synthesis of 4-aminohippuric acid (4-AHA) reduced/stabilized gold nanoparticles and their peroxidase mimicking properties for the colorimetric detection of Fe3+ and Hg2+. The synthesis of nanoparticles was evidenced by appearance of bright red color and an absorption peak at 518 nm. Transmission electron microscopic (TEM) characterization revealed the nanoparticles to be spherical with average size of about 5.9 ± 1.7 nm. X-ray diffraction (XRD) analysis established highly crystalline nature of the nanoparticles. The synthesized nanoparticles have shown very good peroxidase mimicking property; exhibiting the catalytic oxidation of the chromogen 3,3',5,5'-tetramethyl benzidine (TMB) to a blue color product, in the presence of hydrogen peroxide. The peroxidase mimicking activity of the nanoparticles was found to be selectivity enhanced in the presence of Fe3+ and Hg2+ while there was no change in the activity in the presence of other concomitant ions. The mechanism studies revealed that the synthesized gold nanoparticles assisted in electron transfer during the catalytic process however the stimulation of peroxidase-like activity in the presence of Fe3+ and Hg2+ is owed to both generation of hydroxyl radical and accelerated electron transfer. The assay was made selective for iron by the addition of cysteine in acetate buffer; whereas the selective detection of mercury was achieved by carrying out the assay in citrate buffer. The linear ranges for the determination of Fe3+ and Hg2+ in deionized water were found to be: 5-50 ppb and 5-200 ppb respectively. The limits of quantification (LOQ) for Fe3+ and Hg2+ were 4.0 and 2.5 ppb respectively. The assay was applied for the determination of Fe3+ and Hg2+ in drinking and ground water samples. The method holds potential for the on-field screening of these metal ions in real environmental samples.